The most simple form of regularity involves a single class of verbs, a single principal part (the root or a conjugated form in a given person, number, tense, aspect, mood, etc.), and a set of unique rules to produce each form in the verb paradigm. More complex regular patterns may have several verb classes (e. g. distinguished by their infinitive ending), more than one principal part (e. g. the infinitive and the first person singular, present tense, indicative mood), and more than one type of rule (e. g. rules that add suffixes and other rules that change the vowel in the root).
Sometimes it is highly subjective to state whether a verb is regular or not. For example, if a language has ten different conjugation patterns and two of them only comprise five or six verbs each while the rest are much more populated, it is a matter of choice to call the verbs in the smaller groups "irregular".
The concept of regular and irregular verbs belongs mainly in the context of second language acquisition, where the defining of rules and listing of exceptions is an important part of foreign language learning. The concepts can also be useful in psycholinguistics, where the ways in which the human mind processes irregularities may be of interest. However, most other branches of linguistics do not use these categories; historical/comparative linguistics is more interested in categories such as strong and weak.
English regular verbs change their form very little. The past tense and past participle of regular verbs end in -ed, for example:
work, worked, worked
But you should note the following points:
1. Some verbs can be both regular and irregular, for example:
learn, learned, learned
learn, learnt, learnt
2. Some verbs change their meaning depending on whether they are regular or irregular, for example "to hang":
|regular||hang, hanged, hanged||to kill or die, by dropping with a rope around the neck|
|irregular||hang, hung, hung||to fix something (for example, a picture) at the top so that the lower part is free|
3. The present tense of some regular verbs is the same as the past tense of some irregular verbs:
|regular||found, founded, founded|
|irregular||find, found, found|